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Document that WAIT FOR LSN is timeline-blind

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WAIT FOR LSN compares only the numeric LSN and has no notion of which
timeline a WAL record belongs to.  There are many possible scenarios when
timeline-switching can break read-your-writes consistency.  The proper
analysis and timeline support is possible in the next major release.  Yet
just document the current behaviour.

Reported-by: Xuneng Zhou <xunengzhou@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
This commit is contained in:
Alexander Korotkov 2026-05-03 16:20:41 +03:00
parent cb096e6d69
commit 21d290161b
1 changed files with 14 additions and 0 deletions
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doc/src/sgml/ref/wait_for.sgml
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@ -257,6 +257,20 @@ WAIT FOR LSN '<replaceable class="parameter">lsn</replaceable>'
timeline.
</para>
<para>
<command>WAIT FOR</command> compares only the numeric
<acronym>LSN</acronym>; it has no notion of which timeline a WAL
record belongs to. This matters when a standby continues recovery
across an upstream timeline switch &mdash; for example, a cascading
standby whose upstream gets promoted. In that case
<command>WAIT FOR</command> will return <literal>success</literal>
as soon as the position used by the selected wait mode reaches or
passes the numeric <acronym>LSN</acronym>, regardless of which
timeline that <acronym>LSN</acronym> belongs to. Applications that need to
confirm the target refers to the expected timeline must validate
the timeline themselves.
</para>
<para>
On a standby server, <command>WAIT FOR</command> sessions may be
interrupted by recovery conflicts. Some recovery conflicts are